1. Field of the Invention
The present invention relates to methods and means for the extraction of iron from by-product, impure sulfuric acid and/or certain solutions prepared from crystals of iron sulfate and zinc sulfate. The instant process results in the production of a solid product consisting primarily of magnetite and a liquid product comprised of ammoniacal zinc sulfate. The elements contained in the products are among a plethora of plant nutrients normally found in both solid and fluid fertilizers.
Agronomists have classed N, P, and K as primary plant nutrients, Ca, Mg, and S as secondary plant nutrients and Zn, B, Co, Fe, Mn Cu, Na and Mo as micronutrients. Whereas the need for the primary nutrients has been known for decades, the acute need for micronutrients has become apparent only in recent years. Land, in many cases, which has been farmed for relatively long periods of time and fertilized properly with the primary nutrients N, P, and K, has become deficient in some of both the secondary nutrients and micronutrients thereby resulting in low crop yields. In order to restore optimum yields, the level of these nutrients must be brought up to acceptable levels by the addition of the deficient nutrients. (Mortvedt, J. J. et al., "Micronutrients in Agriculture" proceedings of a TVA-sponsored symposium held at Muscle Shoals, Ala., Apr. 20-22, 1971).
1. Description of the Prior Art
Waste acids and sludges have historically been discarded because of the high cost of recovering individual elements therefrom for reuse or sale. However, with the onset of regulations by the EPA in recent years, disposal costs of such materials have risen drastically.
Little work has been done on the recovery of metals or sulfur from galvanizing wastes. Work which has been performed along these lines (Twidwell, L. G. et al, "Recovery of Metal Values from Metal Finishing Hydroxide Sludges by Phosphate Precipitation," proceedings of the Twelfth Annual Research Symposium, Cincinnati, Ohio, Apr. 21-23, 1986) involved the use of relatively dilute solutions, thus making its application to concentrated waste acid unsuccessful. Indeed, in some of our earlier work in which we made attempts, similar to that of Twidwell supra, at phosphate separation of iron, the products resulting therefrom throughout the pH range of 4 to 12 were in the form of gelatinous materials. Oxidation and/or separation of iron or zinc from this material was unsuccessful in all tests using galvanizer acid or solutions prepared from waste crystals due to the formation of such gelatinous materials.
The combination of the nutrients N, S, and Zn is commonly found in a vast number of fluid fertilizers presently being produced on a commercial basis. In order to be used for this purpose, however, the feedstock materials which are to be added for the formulation thereof must be completely solubilized and must not contain materials which would cause precipitation to occur in the final product. For example, a solution of N, S and Zn containing significant amounts of Fe would be undesirable because it is known that the Fe therein would cause solid iron phosphate to form upon its addition to materials containing the primary nutrient phosphorus. For proper utilization as a feedstock in the preparation of dry fertilizers, such material must be compatible with one of the two following types of production processes: (1) for "bulk blends" or "dry mixed" fertilizers, the feedstock material must be granulated to a particle size similar to the material to which it is added (Hoffmeister, George, "Quality Control in a Bulk Blending Plant," Proceedings of the TVA Fertilizer Bulk Blending Conference, Louisville, Ky., Aug. 1-2, 1973); consequently, when materials of the same particle size are used, there will be no physical separation of the ingredients in the blend, and (2) for the production of "compound," "complex," or "cogranulated" fertilizers, the physical properties of the additives are not nearly as important and the feedstock materials may be in the form of a solution, a slurry, or a dry mix comprising relatively small-sized particles. In the manufacture of these type (2) fertilizers, all ingredients are mixed prior to granulation, thus resulting in the production of a fertilizer in which each granule contains, usually homogeneously distributed therethrough, the proportional amount of each separate ingredient comprising the fertilizer.
It will be appreciated by those skilled in this art that many of the limitations and disadvantages associated with endeavors of prior art investigators are now overcome by the practice of the instant invention in which the liquid product resulting therefrom is suitable for direct agricultural application, for mixing into fluid fertilizers, for feeding to a cogranulation fertilizer unit, or for evaporation and granulation to a particle size suitable for bulk blending and in which the solids containing fraction, i.e., the undried magnetite is in a form which can easily be granulated during a subsequent drying step for later addition to a bulk blend fertilizer or can be used wet as a feedstock for a cogranulation produced fertilizer.